Indicator tube



Dec. 4, 1962 J. H. MOCAU LEY 3,067,355

INDICATOR TUBE Filed March 16, 1960 IN VEN TOR.

JOHN H. Mc CHULEY ATTORNEY United States Patent Ofiiice 3,%7,355Patented Dec. 4, 1962 3,067,355 INDICATOR TUBE John H. McCauley,Elizabeth, N.J., assignor to Burroughs Corporation, Detroit, Mich, acorporation of Michigan Filed Mar. 16, 1960, Ser. No. 15,475 8 Claims.(Cl. 3132l0) This invention relates to cold cathode gaseous indicatortubes and particularly to tubes of this type which may be constructedand operated to provide light output of diiferent colors.

Cold cathode gaseous indicator tubes generally include a plurality ofcathode electrodes in the form of indicator characters mounted in asuitable envelope filled with an ionizable gas such as neon, argon, orthe like. Such tubes provide cathode glow having a characteristic colorwhich is determined by the gas filling in the envelope. Presentlyavailable commercial devices of this type produce cathode glow which isgenerally pink, orange, or red. There are many applications in which,for example, blue light is desirable. However, at the present time, acold cathode indicator or readout glow tube providing blue or otherlight output cannot be made simply and inexpensively and in commercialquantities. Accordingly, the principles and objects of the presentinvention are concerned with the provision of an improved cold cathodegaseous indicator glow tube which may be adapted to provide differentcolors of light output.

Briefly, a gaseous cold cathode indicator glow tube, to which theprinciples of the invention are particularly applicable, includes anenvelope in which is mounted a stack of cold cathode indicator glowelectrodes in the form of numerals, letters, or other characters. Eachcathode indicator electrode is adapted to glow when a voltage is appliedbetween it and an anode electrode. The envelope is filled with anionizable gas such as neon and a small quantity of mercury which,together, provide cathode glow which is light orange or light pink incolor.

According to the invention, the characteristic light orange or pinkcathode glow may be changed to an effective white light by raising thetube operating temperature above the typical normal level. With the tubethus operated to provide white light output, any desired color of glowmay be obtained by means of a suitable light filter coupled to the tube.

The invention is described in greater detail by reference to the drawingwherein: a

FIG. 1 is a perspective view, partly in section, of a cold cathodegaseous glow tube embodying the invention; and

FIG. 2 is a sectional, elevational view of a modification of a portionof the apparatus of FIG. 1.

Referring to the drawings, a typical gaseous indicator glow tube 10useful in practicing the invention includes an envelope 12 which hasbeen evacuated of air and filled with a gas suitable for supporting coldcathode glow. Such a gas may be argon, neon, or the like at a suitablepressure which may be in the range of about 30 to about 100 mm. of Hg.The envelope includes a base portion, or stem 14, through which metalbase pins 16 extend and by means of which electrical connection is madeto suitable external electrical circuit elements. Two diametricallyopposed pins 16' are provided with insulated extension posts 18 withinthe envelope and are thus adapted to receive and support the variouselectrode elements of the tube. The envelope 12 also includes atransparent viewing window 20 through which glowing indicator cathodeelectrodes 22 are viewed.

The cathode glow indicator electrodes 22 of the tube 10 may takesubstantially any desired shape; for example, they may be numbers,letters, or the like, and they may be as few in number as desired, or asmany as is practical for the size of the tube. In One form of the tube10 wherein the glow cathode indicator elements are numbers, ten of suchelements are provided, including the numbers 0 to 9. Fewer than ten glowcathodes are shown in FIG. 1 for purposes of simplifying the drawing.The cathode indicator elements 22 are made of any suitable metal, forexample, stainless steel, aluminum, Nichrome, molybdenum, or the like,and they may be made in any suitable fashion, for example, by etching,stamping, or the like.

The cathode elements are provided with diametrically opposed aperturedend tabs (not shown) by means of which they are mounted and supported onthe extension posts 18 of the pins 16'. The cathode elements 22 arestacked on the posts 18 one above the other with their surfaces orientedparallel to each other and transverse to the vertical axis of the tubeand facing the viewing window 20 of the envelope 12. The cathodeelements 22 are mounted with suitable insulating spacers 24 betweenthem, the spacers having sufficient surface area to cover and insulatethe cathode tabs to prevent them from glowingduring operation of thetube. The stack of electrodes is locked on posts 18 by mica rings 26 orthe like.

Each cathode indicator element is provided with a fine wire connectinglead 28 which is welded or otherwise secured at its free end to one ofthe pins 16 within the envelope 12. The leads 28 may be of the samematerial as the numbers, or they may be of any other suitable material.

The tube 10 includes an anode which is preferably in the form of a cup36 having a pair of diametrically opposed longitudinal slots 37 alignedwith the support posts 18 and through which the cathode lead wires 28extend to the pins 16. The stack of cathode electrodes is, in effect,contained within the cup, with the cathode leads 28 and tube pins 16lying outside the cup. The cup 36 rests on, but is insulated from, thepins 16 by an insulating disk 38 of mica or the like. The anode cup isalso electrically connected to one of the pins 16 by a suitable lead(not shown).

The objects of the invention are accomplished by causing the tube 10 togenerate substantially white light and coupling a selected filter to thetube to provide the desired color of light. The desired white light isobtained, according to the invention, by a combination of features inboth tube construction and tube operation. Thus, a small quantity ofmercury is added to the gas in the envelope, say neon, so that, undertypical normal operating conditions, the cathode glow is light orange orlight pink in color. The mercury may be added to the neon filling in anysuitable manner during tube preparation which may follow well-knownprocedures. In one arrangement for carrying out this process, referringto FIG. 2, a small ball of mercury 38 is placed in an evacuatedfrangible capsule 40, of glass or the like, through which a heating wire42 extends. The capsule is sealed in the tube envelope, and at thedesired time in the manufacturing process, heating current is passedthrough the wire, and the mercury is heated and caused to vaporize andcrack the glass capsule. When the capsule cracks, the mercury escapesand condenses on the tube envelope. Alternatively (FIG. 2), a coil 42'of heating wire surrounding the capsule may be used to crack the capsuleand free the mercury.

According to the invention, the typical and normal light pink color ofcathode glow of the tube 10 is con verted to substantially white glow byoperating the tube at an elevated temperature. The desired elevatedtemperature may be achieved by operating the tube at higherthan-normalcathode currents. Thus, with about volts applied between the anode andthe cathodes, a

cathode current of about eight milliamperes provides sufficient heat tocause substantially white cathode glow. Alternatively, elevatedtemperature may be achieved by passing heating current through theheating coil 42'. The heat generated by current in the coil 42 heats thegases in the tube 1!) to the required temperature to provide white lightcathode glow. With the latter method of operation, a normal cathodecurrent level of about two milliarnperes is maintained.

With the tube thus adapted to provide substantially white light, lightof any desired color may be obtained by combinin a suitable opticalfilter with the tube 14 Thus, for example, a sheet 44 of light filteringmaterial is positioned in front of the viewing Window 26 of the tube.Any suitable support means for the filter may be provided. For example,a hollow tube 46 may be secured to the tube envelope l2 and the filtersheet 4-4 may be suitably mounted in the tube.

What is claimed is:

l. A cold cathode gaseous indicator tube assembly comprising an envelopecontaining an anode and an indicator glow cathode adapted to exhibitcathode glow when an appropriate operating potential is applied betweenit and said anode, said cathode glow being provided by a glowing sheathof gas surrounding said cathode, said envelope containing a filling ofan ionizable gas and a smal quantity of mercury suitable for providingsubstantially white cathode glow when said tube is operated at anelevated temperature, and an optical filter in operative relation withsaid cathode.

2. The assembly defined in claim 1 and including circuit means forraising the temperature of the tube in operation.

3. The assembly defined in claim 1 and including auxiliary heating meansinside the tube envelope for raising the temperature of the tube duringits operation.

4. The assembly defined in claim 1 and including an auxiliary heatingwire disposed within the tube envelope for raising the temperature ofthe tube during operation.

5. A cold cathode gaseous indicator tube assembly comprising an envelopehaving a viewing window and containing an anode and a stack of indicatorglow cathodes facing said viewing window, each of said cathodes beingadapted to exhibit cathode glow when an appropriate operating potentialis applied between it and said anode, the cathode glow being provided bya glowing sheath of gas surrounding the cathode, said envelopecontaining a filling of an ionizable gas and a small quantity of mercurysuitable for providing substantially white cathode glow when said tubeis operated at an elevated temperature, and an optical filter coupled tosaid envelope in front of said viewing window, said optical filter beingselected to provide a predetermined color of light output from saidtube.

6. The assembly defined in claim 5 and including auxiliary heating meansinside the tube envelope for raising the temperature of the tube duringits operation.

7. The method of operating a cold cathode gaseous glow tube to providelight output of a selected color, said glow tube including a glowcathode and an anode and a gas filling of an ionizable gas and mercury,the method comprising the steps of applying an operating voltage betweenthe cathode and the anode and thereby causing the cathode to glow withits characteristic color, ieating said tube so that the cathode glow issubstantially White, and optically filtering the desired color from thecathode glow.

8. The method of operating a cold cathode gaseous glow tube to providelight output of a selected color, said glow tube including a glowcathode and an anode and a gas filling of an ionizable gas and mercury,the method comprising the steps of applying an operating voltage betweenthe cathode and anode to provide a level of current flow therebetween atwhich the cathode glows with its characteristic color, increasing thecurrent flow to a higher level at which the temperature of the tube iselevated and the cathode glow is substantially white, and opticallyfiltering a selected color from the cathode glow.

References (Iited in the file of this patent UNITED STATES PATENTS666,602 Couch Jan. 22, 1901 2,068,287 Gabor Jan. 19, 1937 2,479,164Inman Aug. 16, 1949

